The present invention relates to a refrigerant composition suitable for use in compression refrigeration.
Chlorofluorocarbons (CFCs), such as dichlorodifluoromethane (CFC-12), have traditionally been used as refrigerants for compression refrigeration systems. Refrigeration systems that use CFCs as refrigerants generally use mineral oils to lubricate the compressor. These lubricating mineral oils are also known as napthalenic oils. A lubricating mineral oil is typically a lube oil fraction having a viscosity index of from xe2x88x92300 to 140, which has been dewaxed, deasphalted and hydrogenated. The mineral oil may contain up to 15% by weight of an additive such as an antioxidant or a corrosion inhibitor. Typically, it has a kinematic viscosity at 40xc2x0 C. of from 10 mm2/s to 220 mm2/s (10 cSt to 220 cSt).
In compression refrigeration systems it is desirable that all the lubricant should remain in the compressor to ensure that the compressor is adequately lubricated. In practice, however, an amount of lubricant is invariably aspirated into the surrounding pipework of the refrigeration cycle. If the lubricant is insoluble in the refrigerant, there is a danger that it will separate from the refrigerant and fail to return to the compressor. In this event, the compressor becomes inadequately lubricated. Refrigeration systems that use CFCs such as CFC-12 generally use mineral oil lubricants because such CFCs are soluble with the mineral oils throughout the entire range of refrigeration temperatures.
However, recent concern regarding depletion of the ozone layer by CFCs has led to the use of CFCs being restricted. CFC-12 has an ozone depletion potential of 0.9, where the ozone depletion potential of trichloromethane is defined to be 1. Alternative refrigerants are therefore required. Perfluorocarbons are not suitable as alternative refrigerants as they have a high global warming potential (GWP) and excessive atmospheric lifetimes. The GWP is the time-integrated commitment to climate forcing from the instantaneous release of 1 kg of refrigerant expressed relative to that from 1 kg of carbon dioxide, which is taken as having a GWP of 1.
1,1,1,2-tetrafluoroethane (R134a) is becoming widely used as an alternative to chlorofluorocarbon refrigerants. It has substantially no ozone depletion potential. It has a GWP, measured on the basis of a 100 year integrated time horizon, of about 1300. However, R134a has the disadvantage that it is substantially immiscible with the mineral oil lubricants used in existing refrigeration equipment. In other words, R134a cannot be used by itself in such equipment.
Various attempts have been made to find lubricants which can be used with fluorinated hydrocarbons such as R134a. Various polyolesters and polyalkylene glycols have been proposed for this purpose.
Unfortunately, however, these new lubricants are considerably more expensive than the conventional mineral oil lubricants. Also, they are often hydroscopic and absorb atmospheric moisture. Clearly, in order to minimise the changes necessary to the equipment or operating conditions when replacing CFCs in compression refrigeration systems with alternative refrigerants, it is desirable to be able to use the conventional mineral oils as used with the CFCs.
There is therefore a demand for a refrigerant which possesses the desirable properties of R134a but which can be used with the conventional mineral oil lubricants as used with the CFCs. Existing refrigerants which can be used with the mineral oil lubricants are invariably deficient in some other respect.
A novel refrigerant composition has now been devised, according to the present invention, which has substantially no ozone depletion potential, which is sufficiently compatible with the conventional mineral oil lubricants to be used with them and which has an operating performance equal to or superior to fluorinated hydrocarbons such as R134a and chlorofluorocarbons such as CFC-12.
The present invention provides a non-azeotropic refrigerant composition having a vapour pressure at xe2x88x9220xc2x0 C. of from 70 to 190 kPa (0.7 to 1.9 bar), at +20xc2x0 C. of from 510 to 630 kPa (5.1 to 6.3 bar) and at +60xc2x0 C. of from 1620 to 1740 kPa (16.2 to 17.4 bar), which composition comprises:
(a) 1,1,2,2-tetrafluoroethane (R134), 1,1,1,2-tetrafluoroethane (R134a), difluoromethoxytrifluoromethane (E125) or a mixture of two or more thereof, in an amount of from 60 to 99% by weight, based on the weight of the composition;
(b) from 1 to 10% by weight, based on the weight of the composition, of an unsubstituted hydrocarbon of the formula CnHm in which n is at least 4 and m is at least 2nxe2x88x922; and,
(c) up to 39% by weight, based on the weight of the composition, of a vapour pressure depressant,
Typically, a composition is xe2x80x9cnon-azeotropicxe2x80x9d if, at any given pressure and temperature, the composition of the liquid and the composition of the vapour above the liquid are substantially not equal. Thus, any loss of vapour from a non-azeotropic composition will result in a composition change of the remaining liquid. In contrast, loss of vapour from an azeotrope does not result in a change of liquid composition.
Preferred non-azeotropic compositions are those in which, after about 50% of the composition is removed such as by evaporation or boiling off, the difference in the original composition and the composition remaining is more than about 2%, more preferably more than about 10%.
Typically, component (a) is present in an amount of from 70 to 95%, preferably from 80 to 90%, more preferably from 82 to 86%, by weight based on the composition.
Component (b) is an unsubstituted hydrocarbon of the formula CnHm, in which n is at least 4 and m is at least 2nxe2x88x922. Typically, n is from 4 to 6, preferably 4 or 5. Typically, the unsubstituted hydrocarbon has no triple bonds. Preferably, the unsubstituted hydrocarbon is saturated except for one double bond. More preferably, the unsubstituted hydrocarbon is fully saturated.
Typically, the unsubstituted hydrocarbon is methylenecyclopropane, 1-butene, cis and trans-2-butene, butane, 2-methyl propane, cyclopentene, cyclopentane, 2-methyl-1-butene, 2-methyl-2-butene, 3-methyl-1-butene, 1-pentene, cis and trans-2-pentene, 2-methylbutane, pentane or a mixture of two or more thereof. Preferably, it is cyclobutane, more preferably n-butane (R600) or 2-methyl-propane (R600a).
Typically, the unsubstituted hydrocarbon is present in an amount of from 1 to 8%, preferably from 2 to 6%, more preferably from 2 to 5%, by weight based on the composition.
The unsubstituted hydrocarbon serves to improve the compatibility of the refrigerant composition of the invention with mineral oil lubricants. Unfortunately it increases the vapour pressure of the composition of the invention. It may also increase the flammability of the composition of the invention.
Accordingly, component (c) is required in order to reverse the increase in vapour-pressure caused by component (b). Component (c) is a vapour-pressure depressant, i.e. a compound capable of lowering the vapour pressure of the refrigerant composition.
Typically, the vapour-pressure depressant is 1,1-difluoroethane, 1,1,1,2,2,3,3-heptafluoropropane, 1,1,1,2,3,3,3-heptafluoropropane, octafluorocyclobutane, 1,1,1,2,2-pentafluoropropane, 1,1,2,2,3-pentafluoropropane, trifluoromethoxymethane, trifluoromethoxypentafluoroethane, difluoromethoxypentafluoroethane, trifluoromethoxy-1,2,2,2-tetrafluoroethane, fluoromethoxytrifluoromethane, difluoromethoxymethane, pentafluoroethoxypentafluoroethane, difluoromethoxydifluoromethane, trifluoromethoxy-2,2,2-trifluoroethane, fluoromethoxymethane, difluoromethoxy-1,2,2,2-tetrafluoroethane, fluoromethoxyfluoromethane, difluoromethoxy-2,2,2-trifluoroethane, methoxy-2,2,2-trifluoroethane, methoxy-1,1,2,2-tetrafluoroethane or a mixture of two or more thereof. Preferably it is 1,1-difluoroethane (R152a), 1,1,1,2,2,3,3-heptafluoropropane (R227ca), 1,1,1,2,3,3,3-heptafluoropropane (R227ea), 1,1,1,2,2-pentafluoropropane (R245cb), octafluorocyclobutane (RC-318) or a mixture of two or more thereof.
Component (c) is typically present in an amount of from 4 to 29%, preferably from 8 to 18%, more preferably from 12 to 16%, by weight based on the composition. The amount of vapour-pressure depressant depends on the nature and amount of components (a) and (b). If a large amount of component (b) is present (i.e. more than about 5% by weight, based on the composition), then a correspondingly greater amount of component (c) (or of R134) will be required to achieve an appropriate vapour pressure.
The amount of component (c), if any, should be such that the composition has a vapour pressure at xe2x88x9220xc2x0 C. of from 70 to 190 kPa, preferably from 90 to 190 kPa, more preferably from 120 to 180 kPa, at 20xc2x0 C. of from 510 to 630 kPa, preferably from 530 to 630 kPa, more preferably from 580 to 620 kPa, and at 60xc2x0 C. of from 1620 to 1740 kPa, preferably from 1630 to 1720 kPa, more preferably from 1650 to 1700 kPa. This amount can, of course, be readily determined by routine experiment. It is particularly preferred that the vapour pressure depressant is present in an amount so that the composition has a vapour pressure substantially equal to that of R134a.
When the vapour-pressure depressant is present in an amount of more than 20% by weight, based on the weight of the composition, it is preferred that the vapour-pressure depressant comprises two or more compounds, each of which being present in an amount of 20% by weight or less, based on the weight of the composition.
The refrigerant composition of the invention may further comprise component (d), a flammability supressant. Preferably, the composition comprises a flammability supressent when the unsubstituted hydrocarbon (b) is present in an amount greater than about 2% by weight based on the composition. It is particularly preferred that the composition comprises a flammability supressent when the unsubstituted hydrocarbon (b) is present in an amount of about 3% by weight or more based on the composition. Thus compositions which do not contain a flammability supressent typically contain less than 3%, for example from 1 to 2% by weight of the hydrocarbon (b) based on the composition.
Typically the flammability supressant is 1,1,1,2,2,3,3-heptafluoropropane, 1,1,1,2,3,3,3-heptafluoropropane, octafluorocyclobutane, octafluoropropane, trifluoromethoxytrifluoromethane, difluoromethoxytrifluoromethane, trifluoromethoxypentafluoroethane, difluoromethoxypentafluoroethane, trifluoromethoxy-1,2,2,2-tetrafluoroethane, or a mixture of two or more thereof. The vapour-pressure depressant may also function as a flammability supressant. Vapour-pressure depressants which also function as flammability supressants include 1,1,1,2,2,3,3-heptafluoropropane (R227ca), 1,1,1,2,3,3,3-heptafluoropropane (R227ea), octafluorocyclobutane (RC-318) trifluoromethoxypentafluoroethane (E218), difluoromethoxypentafluoroethane (E227ea) and trifluoromethoxy-1,2,2,2-tetrafluoroethane (E227ca).
If component (d) is present, components (c) and (d) are typically together present in an amount of up to 39%, preferably from 4 to 29%, more preferably from 8 to 18%, most preferably from 12 to 16%, by weight based on the composition. Typically, when component (d) is present, component (c) is present in an amount of up to 19% by weight, based on the composition and component (d) is present in an amount of up to 20% by weight, based on the composition.
When the flammability supressant and the vapour-pressure depressant are together present in an amount of 20% by weight or more, based on the weight of the composition, it is preferred that no single compound comprised in the flammability supressant or vapour-pressure depressant is present in an amount of 20% by weight or more, based on the weight of the composition.
Clearly, any flammability supressant or vapour-pressure depressant used must not render the refrigerant composition unsuitable for use in compression refrigeration. Thus, the choice of vapour-pressure depressant or flammability supressant should not be such as to significantly decrease solubility in the mineral oil lubricants. Typically, addition of the vapour-pressure depressant or flammability supressant causes no more than a 10%, preferably no more than a 5%, decrease in the solubility of the composition in the mineral oil lubricants.
Typically, any flammability supressant or vapour-pressure depressant used should have a GWP, measured on the basis of a 100 year integrated time horizon, of less than 5,000, preferably less than 4,000, most preferably less than 3,500.
In addition, any flammability supressant or vapour-pressure depressant used should not impart undue toxicity to the refrigerant composition. The Occupational Exposure Limit (OEL) of the refrigerant composition of the invention is typically from 800 to 1000, preferably from 850 to 950, ppm.
The flammability supressant and vapour pressure depressant should have substantially no ozone depletion potential.
Furthermore, the flammability supressant and/or vapour-pressure depressant should not unduly decrease the operating performance of the refrigerant composition of the invention. Typically, the cooling capacity of a compression refrigeration apparatus, using, as refrigerant, the composition of the invention, is not more than 10% less, preferably not more than 5% less, more preferably not less than, the cooling capacity of an identical compression refrigeration apparatus, operating under identical conditions, using, as refrigerant, CFC-12 or R134a.
Typically, the refrigerant composition of the invention contains substantially no lubricant such as polyalkylene glycol.
Typically, the energy consumption of a compression refrigeration apparatus using, as refrigerant, the composition of the invention, is not more than 10% less, preferably not more than 5% less, more preferably not less than, the energy consumption of an identical compression refrigeration apparatus, operating under identical conditions, using, as refrigerant, CFC-12 or R134a.
The following compositions are particularly preferred:
1) compositions in which component (a) is R134 and/or R134a, component (b) is R600 and/or R600a and component (c) is R152a, R227ca, R227ea or a mixture of two or more thereof;
2) compositions in which component (a) is R134 and/or R134a, component (b) is R600 and/or R600a and component (c) is R152a;
3) Compositions in which component (a) is R134 and/or R134a, component (b) is R600 and/or R600a and component (c) is R227ca and/or R227ea.
Typically, in the refrigerant composition of the present invention, the ratio of the total number of fluorine atoms in the composition to the total number of hydrogen atoms in the composition is desirably at least 1.25:1, preferably at least 1.5:1, more preferably at least 2:1. Typically, the refrigerant composition has a lower flammable limit (LFL) of more than 7% v/v in air, preferably, a LFL of more than 14% v/v in air. Most preferably, the refrigerant composition is non-flammable.
Preferably, the refrigerant composition of the present invention has a vapour pressure substantially equal to that of R134a. R134a has a vapour pressure at xe2x88x9220xc2x0 C. of about 134 kPa (5 psi.g), at 20xc2x0 C. of about 572 kPa (68 psi.g) and at 60xc2x0 C. of about 168 kPa (229 psi.g). Typically, the composition of the invention has a vapour pressure not exceeding xc2x160 kPa (0.6 bar), preferably not exceeding xc2x140 kPa (0.4 bar) of that of R134a between xe2x88x9230xc2x0 C. and +60xc2x0 C.
The refrigerant composition of the invention has substantially no ozone depletion potential. Typically, it has a global warming potential (GWP), measured on the basis of a 100 year integrated time horizon, of less than 2000, preferably less than 1600, more preferably less than 1300.
The refrigerant composition of the present invention is preferably used in a domestic refrigeration apparatus. Typically, it is used in a compression refrigeration apparatus which contains not more than 1 kg of refrigerant.
The present invention also provides a process of producing refrigeration, comprising condensing a composition of the invention and thereafter evaporating the composition in the vicinity of a body to be cooled.
The refrigerant composition of the present invention can be prepared by transferring the individual components by autogenous pressure into an initially evacuated pressure vessel, in order of ascending vapour pressure at room temperature. The amount of each component can be checked by weighing the vessel and contents before and after transferring it.
The refrigerant composition of the present invention is advantageous as it does not deplete the ozone layer, it has a low global warming potential (GWP) relative to CFC-12 or R134a, it is compatible with mineral oil lubricants and it has an operating performance equal to or superior to conventional refrigerants such as R134a and CFC-12.
The refrigerant composition of the present invention is compatible with the mineral oil lubricants as used with CFC refrigerants. Prior to the present invention it was thought that, for a refrigerant and lubricant to be compatible, the liquid phases must be miscible. However, it has now surprisingly been found that satisfactory results are achieved if gaseous refrigerant is at least partly soluble in the liquid lubricant. Although the refrigerant composition of the present invention is not fully miscible with mineral oil lubricants when in its liquid phase, in the gaseous phase it is partially soluble in the mineral oil. The refrigerant composition of the invention is thus compatible with mineral oil lubricants.
The refrigerant composition also has a high operating performance. Refrigeration systems containing the composition of the present invention are up to 10% more efficient than refrigeration systems containing conventional refrigerants.
It is surprising that the above advantages are achieved by the refrigerant composition of the present invention because the refrigerant composition is a blend of fluorohydrocarbons and hydrocarbons rather than a single compound. Prior to the present invention it was thought to be undesirable to use non-azeotropic mixtures as refrigerants as these mixtures show a temperature glide. A temperature glide of a mixture is the absolute value of the difference between the starting and ending temperatures of the gas/liquid phase change by the mixture. It can be measured by determining the difference between the bubble point of the mixture (the temperature at which the mixture of liquids starts to boil) and the dew point of a corresponding mixture of gases (the temperature at which the mixture of gases starts to condense).
Temperature glide was thought to lead to variable temperatures in the evaporator of a compression refrigeration system and hence was thought to be undesirable. However, although the refrigerant compositions of the present invention are found to have up to a 9 K temperature glide when tested in the laboratory, it has surprisingly been found that the temperature of an evaporator of a domestic refrigeration system containing the refrigerant composition of the present invention is substantially constant.